1. Field of the Invention
This invention relates to a process for the production of detergent compositions in particulate or powder form. More particularly it relates to the production of detergent compositions containing mixtures of anionic and nonionic detergent-active materials, by means of the spray-drying technique.
2. The Prior Art
The production of detergent compositions in particulate or powder form by spray-drying an aqueous slurry of detergent ingredients from nozzles located on a ring manifold placed in the upper portion of a spray-drying tower is known. The slurry is sprayed in a plurality of droplets which are dried to solid particles by the action of the drying gas passing through the spray-tower.
Detergent powders, particularly for fabric washing purposes generally contain 5-60% by weight, of active-detergent materials, 5-80% of builders, detergency improvers etc., and 0-50% of fillers and other additives. The normally used detergent-active compounds are anionic or nonionic in character but they may also be cationic or amphoteric, if desired.
The slurry-making and spray-drying of phosphate builder containing compositions generally do not present difficulties so long as the active-detergent component is not a mixture of different actives. The resulting powders of simple anionic compositions have normally satisfactory physical properties, i.e. they are sufficiently free-flowing and have very small tendency to caking on storage. However, combinations of two or more detergent-active compounds are often preferred to achieve optimal properties, e.g. as regards detergency action and/or foaming characteristics. Sometimes even more complex active mixtures may be desirable for specific purposes. The most commonly used active-detergent combination in the last decade includes a mixture comprising anionic synthetic non-soap detergents, fatty acid soaps and nonionic detergents.
Many of the present day heavy-duty detergent compositions having controlled sudsing characteristics suitable for use in drum-type washing machines comprise this typical active-detergent mixture or at least a mixture of anionic and nonionic synthetic detergents.
It has been observed that the conventional processing of the afore-mentioned "mixed-active" detergent compositions presents a number of problems, resulting also in unsatisfactory powders, which in many cases are unacceptable. In the conventional manner slurries are prepared either batch-wise, semi-cntinuously or continuously, but in all cases all the ingredients are mixed to one slurry with the sodium tripolyphosphate builder generally added at the end. The main problems one may be faced with when processing "mixed-active" detergent formulations are due to:
(1) Undesirable rheological properties of the slurry, such as high slurry viscosities; PA0 (2) Separation of slurries in two or more liquid and solid phases; PA0 (3) Poor solubility of powder; PA0 (4) Poor free-flowing property and softness of powder and tendency to caking PA0 (5) Sensitivity of slurry and powder properties to small variations in the formulation, e.g. slurry viscosity, powder bulk density, solubility, free-flowiness.
Some of these problems could possibly be overcome or at least be influenced by the use of special measures. The addition of more water into the slurry reduces slurry viscosities, though obviously this would result in more spray-drying energy to evaporate additional water, reducing spray-tower capacity and still possibly give wet powders. The formation of small sodium tripolyphosphate hexahydrate crystals could have an improved effect on the free-flowing property of the powder. Better agitation would keep the slurry more homogeneous and possibly reduce the tendency to separate. Bulk density could be influenced by aeration or deaeration of the slurry.
Appart from the fact that these measures are each specifically directed to a particular aspect and which cannot always be altogether successfully applied to overcome the complex of problems, there are some more problems that cannot be solved by the conventional techniques. The possibility of using active-detergent mixtures in every variation and in all ratios, as desirably wanted for various performance reasons, has hitherto been restricted to a great extent, because the slurries cannot be properly processed in existing plants, even when the above measures are taken into account. It has also been observed that the above measures are not effective at all to overcome the stickiness of powders comprising certain mixtures of active-detergent materials. This lack of flexibility will be even more serious when the present tendency is considered to decrease the content of phosphates, particularly condensed phosphate detergency builders, such as sodium tripolyphosphate in detergent compositions, because of suggestions that such use of phosphates contributes to eutrophication. The corrective influence of the sodium tripolyphosphate hexahydrate crystals on powder properties will decrease when part of the phosphate is omitted or replaced by other non-phosphate builders, particularly organic builders.